Apply the trigonometric identity: $\tan\left(\theta \right)^n$$=\frac{\sin\left(\theta \right)^n}{\cos\left(\theta \right)^n}$, where $n=2$

Divide fractions $\frac{\cos\left(x\right)}{\frac{\sin\left(x\right)^2}{\cos\left(x\right)^2}}$ with Keep, Change, Flip: $a\div \frac{b}{c}=\frac{a}{1}\div\frac{b}{c}=\frac{a}{1}\times\frac{c}{b}=\frac{a\cdot c}{b}$

Combine fractions with common denominator $\sin\left(x\right)^2$